This invention relates to a compressor, and its method of operation, in which a noncompressible fluid is pumped back and forth between a pair of chambers to compress a source of compressible fluid.
Compressors are used in many different applications. The most common type of compressor is the air compressor which compresses atmospheric air. However, other fluids are commonly compressed, such as refrigerant in a refrigeration system. Compressors come in many sizes and shapes, depending on the fluid being compressed and the pressure and volume requirements, however, all prior art positive displacement compressors use solid elements to compress the fluid. The use of solid elements to affect compression limits the compressor's efficiency, makes it complex, and results in high maintenance costs. In addition, with compressors using solid compression elements it is difficult to prevent oil, microscopic particles, and water from ending up in the compressed fluid.
Two factors limit the volumetric efficiency of compressors using solid compression elements. First it is necessary to maintain some clearance between the solid element and the structure against which it compresses fluid so that they will never come into contact with one another due to thermal expansion, even under the most severe operating conditions. Thus, a portion of the cylinder volume necessarily is not utilized during compression. Second, compression of fluid causes its temperature to increase, and heat then is transferred from the fluid into the parts of the compressor, such as the piston head, the compressor chamber walls, and the chamber head, which surround the fluid. Thus, the temperature of these parts increases also. Then when new fluid is drawn into the compressor it is heated by those hot compressor parts which causes the fluid to expand and become less dense. Thus, less fluid is available for compression and the volumetric efficiency is reduced. Because of this phenomenon, compressors typically are cooled in one fashion or another. However, with a compressor that uses a solid compression element, such as a piston, this element is usually buried in the compressor and is difficult to cool.
In addition, air, and other compressible fluids, typically contains moisture, and when the fluid is compressed this moisture condenses out. Because compressors with solid compression elements pass whatever is drawn into them back out in the compressed fluid, moisture must be removed from the compressed fluid by passing the fluid through a drier. This not only is expensive but adds to the complexity of the compressor and of its operation. In addition any microscopic particles of material which are too small to be removed by filtering remain in the compressed fluid.
Furthermore, the majority of compressors require lubrication, and with compressors using solid compression elements lubricating oil will adhere to the compression element and be thrown off of it during operation of the compressor, resulting in oil in the compressed air. This is particularly true with reciprocating piston compressors where there is rapid deceleration of the piston at the top of each stroke which causes oil to be thrown into the compressor outlets where it is easily entrained in the compressed fluid as the fluid flows through the outlets at a high rate of speed.
Another shortcoming of many prior art compressors, and in particular with piston compressors, is that when they are stopped mid-stroke, partially compressed fluid must be bled from the cylinder before the compressor is restarted. As a result the energy that went into this partial compression is lost. In addition, for reasons of safety, health, and environmental protection, many gases cannot be expelled into the atmosphere. Thus, the expelled gas must be contained by add-on equipment and re-introduced into the compressor at an obvious premium in original cost and maintenance cost.
Finally, compressors having solid compression elements typically have many moving parts, most of which are subject to high loading. Thus, they are expensive to build and maintain. In addition, they require periodic maintenance which causes the compressor to be out of service for extended periods of time on a regular basis.
The subject invention overcomes the foregoing shortcomings and limitations of compressors having solid compression elements by fluidly interconnecting a pair of hollow chambers through a conduit system. A noncompressible transfer fluid fills one of the chambers and the conduit system, and a pump located in the conduit system is used to pump the transfer fluid back and forth between the chambers. A switching system, associated with the conduit system, causes the pump to pump transfer fluid into a first one of the chambers until that chamber becomes completely filled, and then pump transfer fluid from the first chamber back into the second chamber until the second chamber becomes completely filled. This cycle is repeated during the operation of the pump.
Each chamber has a compressible fluid inlet through which compressible fluid is drawn into the chamber when transfer fluid is being pumped out of it, and a compressible fluid outlet through which compressible fluid is discharged from the chamber as the chamber is filled with the transfer fluid. One-way valves, located in the compressible fluid inlets and outlets prevent the compressible fluid from flowing through them in the reverse direction. A storage tank that is fluidly connected to the compressible fluid outlets receives and stores the compressed fluid. A heat exchanger located in the conduit system cools the transfer fluid as it is being pumped between the two chambers.
In a preferred embodiment of the invention, the conduit system includes a first conduit that extends between the first chamber and the pump outlet, and has a first valve located in it. A second conduit, having a second valve located in it, extends between the pump inlet and the second chamber. In addition, a third conduit extends between the second chamber and the pump outlet and a fourth chamber extends between the pump inlet and the first chamber. The third conduit has a third valve located in it, and the fourth conduit has a fourth valve located in it.
The switching system includes a first level sensor that is located at the uppermost level of the first chamber, and a second level sensor that is located at the uppermost level of the second chamber. The level sensors are activated whenever their respective chambers are filled with transfer fluid. The level sensors are connected to a microprocessor that is programmed to open the first and second valves and close the third and fourth valves when the first level sensor is activated, and close the first and second valves and open the third and fourth valves when the second level sensor is activated. Thus, the direction of transfer fluid flow through the conduit system automatically reverses each time one of the chambers is filled.
The invention also includes a bleed system that removes excess transfer fluid from the compressor whenever it overfills as a result of absorbing water that condensates out of the fluid as it is compressed. In the preferred embodiment, the bleed system includes a third level sensor, that is located a predetermined distance above the bottom of the second chamber. The third level sensor is activated whenever the transfer fluid fills the second chamber to this predetermined level. A bleed outlet, located in the bottom of the second chamber, has a fifth valve located in it. The fifth valve, which is normally closed, is opened by the microprocessor whenever the first and third level sensors are simultaneously activated. The microprocessor is programmed to close the fifth valve again when it has been open for a predetermined time interval. During this time interval, transfer fluid is pumped out of the conduit system through the bleed outlet as it is pumped out of the first chamber and into the second chamber.
Accordingly, it is a principal object of the subject invention to provide a compressor that uses noncompressible transfer fluid as its piston.
It is a further object of the subject invention to provide such a compressor in which the entire volume of the compression chamber is utilized to compress fluid on each stroke.
It is a still further object of the subject invention to provide such a compressor in which the transfer fluid is cooled outside of the compression chambers between every stroke.
It is yet a further object of the subject invention to provide such a compressor in which partially compressed air does not have to be bled out of the chamber in order to restart the compressor, when it is stopped in mid-stroke.
It is a still further object of the subject invention to provide such a compressor which automatically removes moisture that condenses in the compressible fluid during compression.
It is a further object of the subject invention to provide such a compressor in which microscopic particles in the air being compressed are removed during compression.
The foregoing and other objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.